Though cities occupy only a small percentage of Earth's terrestrial surface, humans concentrated in urban areas impact ecosystems at local, regional and global scales. I examined the direct and indirect ecological outcomes of human activities on both managed landscapes and protected native ecosystems in and around cities. First, I used highly managed residential yards, which compose nearly half of the heterogeneous urban land area, as a model system to examine the ecological effects of people's management choices and the social drivers of those decisions. I found that a complex set of individual and institutional social characteristics drives people's decisions, which in turn affect ecological structure and function across scales from yards to cities. This work demonstrates the link between individuals' decision-making and ecosystem service provisioning in highly managed urban ecosystems.
Second, I examined the distribution of urban-generated air pollutants and their complex ecological outcomes in protected native ecosystems. Atmospheric carbon dioxide (CO2), reactive nitrogen (N), and ozone (O3) are elevated near human activities and act as both resources and stressors to primary producers, but little is known about their co-occurring distribution or combined impacts on ecosystems. I investigated the urban "ecological airshed," including the spatial and temporal extent of N deposition, as well as CO2 and O3 concentrations in native preserves in Phoenix, Arizona and the outlying Sonoran Desert. I found elevated concentrations of ecologically relevant pollutants co-occur in both urban and remote native lands at levels that are likely to affect ecosystem structure and function. Finally, I tested the combined effects of CO2, N, and O3 on the dominant native and non-native herbaceous desert species in a multi-factor dose-response greenhouse experiment. Under current and predicted future air quality conditions, the non-native species (Schismus arabicus) had net positive growth despite physiological stress under high O3 concentrations. In contrast, the native species (Pectocarya recurvata) was more sensitive to O3 and, unlike the non-native species, did not benefit from the protective role of CO2. These results highlight the vulnerability of native ecosystems to current and future air pollution over the long term. Together, my research provides empirical evidence for future policies addressing multiple stressors in urban managed and native landscapes.
Permafrost degradation is leading to rapid wetland formation in northern peatland ecosystems, altering the role of these ecosystems in the global carbon cycle. I reviewed the literature on the history of the MPP theory, including tracing its origins to The Second Law of Thermodynamics. To empirically test the MPP, I collected soils along a gradient of ecosystem development and: 1) quantified the rate of adenosine triphosphate (ATP) production--literally cellular energy--to test the MPP; 2) quantified greenhouse gas production (CO2, CH4, and N2O) and microbial genes that produce enzymes catalyzing greenhouse gas production, and; 3) sequenced the 16s rRNA gene from soil microbes to investigate microbial community composition across the chronosequence of wetland development. My results suggested that the MPP and other related theoretical constructs have strong potential to further inform our understanding of ecosystem development. Soil system power (ATP) decreased temporarily as the ecosystem reorganized after disturbance to rates of power production that approached pre-disturbance levels. Rates of CH4 and N2O production were higher at the newly formed bog and microbial genes involved with greenhouse gas production were strongly related to the amount of greenhouse gas produced. DNA sequencing results showed that across the chronosequence of development, the two relatively mature ecosystems--the peatland forest ecosystem prior to permafrost degradation and the oldest bog--were more similar to one another than to the intermediate, less mature bog. Collectively, my results suggest that ecosystem age, rather than ecosystem state, was a more important driver for ecosystem structure and function.
the past half century due to demographic changes. The increase in meat is visible in Mexico as well due to expanding economic interest in cattle production plus increased population and rising incomes. The worst consequences of our modern food system are in factory farming of animals, which requires a greater amount of resources than for producing grains, fruits, and vegetables. The specific effects of meat consumption highlight the importance of understanding humans as actors in the food system. In order to explore the drivers of consumer food and meat choice, my research answered the two questions: What factors influence meat consumption? and How do cultural and social norms influence decisions to consume certain types and amounts of meat?
Qualitative interviews were conducted with Mexican-American respondents between age 20 and 29 as the population of interest because of their regional dominance in the study area of Tempe, AZ and because of the high prevalence of meat in their cultural diets. Looking at millennials in particular is crucial because as the first generation born with technology and Internet as constants, they have formed unique characteristics like openness to change and new perspectives. My sample population communicated motivations and constraints to their overall consumption patterns and the frequency and types of meat consumed.
This study found that cost and convenience were the driving factors behind food choice, given the hectic schedules of the sample population, who were mostly students at Arizona State University. Culture played an important role in respondents' heavy meat consumption given their exposure to meat's centrality in traditional Mexican meals. Acculturation did not play an extensive role because prominent Mexican culture in the Southwest U.S. allowed respondents' families access to traditional food while living in the US. The lack of sustainability knowledge and its connection to food choice indicates the importance of marketing that contextualizes decreased meat consumption. Rather than focusing solely on environmental outcomes, marketing tools highlighting health, financial, and economic benefits of eating less meat would encourage more consumers to decrease consumption.
Across governance scales, my analysis found that informational and contentious interactions occur around water management plans, groundwater withdrawal fees, and growth debates due to the stipulations of Arizona’s Groundwater Management Act. Locally, municipalities in different groundwater basins coordinate by pooling resources for water development due to shared growth visions. However, municipalities within the same groundwater basin are divided in their pursuit of the state-mandated goal of safe yield due to discontent arising from differing growth visions, libertarian values of water control, and unequal responsibilities among actors in conserving water or monitoring use. Finally, local and state actors exercise power through litigation, legislation, and political processes to pursue their interests, thereby limiting coordination for water sustainability.
My explicit analysis of power reveals that coordination occurs not just because of water policies but due to interest-based water narratives (growth and libertarian). The emphasis of growth proponents on supply augmentation and libertarian opposition to regulations pose significant barriers to water sustainability. Successful policy-based pursuits of water sustainability will, thus, require an acknowledgment of these management asymmetries and commitments to addressing them.